The present invention relates to a catalyst composition and to the related process for its use in the production of acetaldehyde by the hydroformylation of methanol with carbon monoxide and hydrogen.
The dwindling reserves of crude oil and the uncertainty of availablility of crude oil supplies has led to research for the exploitation of coal, natural gas and other organic materials as the source of organic chemicals traditionally derived from petroleum. It is known that these materials can be used to produce a gas mixture of carbon monoxide and hydrogen known as synthesis gas and that systhesis gas can be used to make methanol, which can be further reacted through homologation and hydroformylation reactions with more synthesis gas in the presence of catalysts to produce other chemicals. Among these other chemicals is acetaldehyde, an organic chemical compound of considerable importance as an intermediate in the production of, for example, ethanol, acetic acid, acetic anhydride, ethyl acetate, butyraldehyde, and butanol as well as other derivatives.
There are various catalyst systems known for use in acetaldehyde-producing processes using the hydroformylation reaction, with many based on cobalt and using a halide promoter. These catalyst systems can be judged on the basis of activity, selectivity, and stability (as defined below). It is desirable that all of these values remain high while minimizing corrosion of the equipment used; however, it is often true that an increase of one of these values will have a detrimental effect on one or more of the others or increase the equipment corrosion. Thus, a catalyst system that displays high values for activity, selectivity, and stability with minimal corrosion would be an improvement over catalysts heretofore disclosed.
"Activity" as used herein denotes the term that relates to the amount of reactants the catalyst can convert per unit volume per unit time. The reactants being carbon monoxide, hydrogen and methanol. The activity can be determined by measuring the rate in which the acetaldehyde product is made. It is important that the reaction be carried out at a sufficiently rapid rate for it to be commercially acceptable.
"Selectivity" as used herein denotes the amount of desired organic products as opposed to other organic by-products formed by the catalyzed reaction. In the production of acetaldehyde, other organic by-products are formed; the main such by-products being ethanol, methyl acetate and methane.
"Stability" as used herein denotes the length of time a catalyst will function before losing its catalytic activity.
"Conversion" as used herein denotes percentage of initially charged methanol converted to acetaldehyde and/or other organic products.
"Realizable acetaldehyde" as used herein denotes the sum of the free acetaldehyde produced plus the amount of acetaldehyde recoverable from 1,1-dimethoxyethane formed during the reaction.
"Corrosion" as used herein denotes the gradual loss of weight or thickness of the materials of construction of the equipment or of the loss of structural integrity of the walls thereof, during the course of the reaction. At the conditions often encountered in carbonylation, hydroformylation and homologation reactions, most halide promoted catalyst systems are corrosive towards metal typically used in these systems leading to an undesirably short life or the need to use expensive materials that do not corrode as readily. It is, therefore, desirable to provide a catalyst system that not only has acceptable activity, selectivity and stability but one that is also less corrosive to the equipment.
The importance of employing catalyst systems containing specifically defined concentrations of components to minimize equipment corrosion and simultaneously enhance activity, selectivity and stability has not heretofore been recognized even though extensive literature exists on the use of halide-promoted, cobalt-based catalysts systems in the carbonylation, hydroformylation, and homologation reactions involving synthesis gas.
Thus, in U.S. Pat. No. 3,356,734 issued to M. Kuraishi et al. on Dec. 5, 1967, there is disclosed a cobalt-iodide catalyst system for the hydroformylation of methanol to produce acetaldehyde. The process, however, exhibits low methanol conversions and low selectivity to acetaldehyde, and there is no recognition indicated of the corrosion problem, nor do they use a phosphorus compound or inert solvent in the reaction.
In U.S. Pat. No. 4,151,208 issued to Pretzer et al. on Apr. 24, 1979, the catalyst system for the production of acetaldehyde is cobalt (II) mesotetraaromaticporphine and an iodine promoter. There is no reference to the use of a phosphorus compound or an inert solvent, nor any mention of the corrosion problem and its resolution.
Japanese Publications No. JA 77/136110 and JA 77/136111 both by Saito et al. and published on Nov. 14, 1977, disclose processes for making aldehydes using catalyst systems containing cobalt, a halogen element and a phosphorus compound. These processes exhibit low selectivity towards acetaldehyde. There is also no recognition of the corrosion problem nor do they disclose the use of an inert solvent in the reaction.
European patent application No. 10,373 by British Petroleum Company Limited and published on Apr. 30, 1980, discloses processes for making ethanol or acetaldehyde using a catalyst system containing cobalt, an iodide or bromide and a polydentate ligand wherein the donor atoms are selected from nitrogen, phosphorus, arsenic, antimony and bismuth. The methanol may be reacted with synthesis gas in the presence of an acid or acid derivative, or an inert liquid which is an aryl halide, a thiophene, a long chain acid or a silicon oil. The predominant product is ethanol when the donor atoms of the polydentate ligand are exclusively nitrogen or phosphorus, particularly phosphorus. The predominant product is acetaldehyde when the donor atoms are exclusively arsenic, antimony or bismuth. There is no reference to the effect of the cobalt and halide catalyst components and the inert diluent nor is there reference to the effect of their relative concentrations on acetaldehyde selectivity or activity. This application teaches away from a catalyst system containing a phosphine and also having high selectivities and activities for acetaldehyde. Particularly, this application shows no appreciation for the necessity of using the entire combination; a source of cobalt, a halide, a phosphorus compound and an inert diluent; at defined concentrations and ratios to obtain high activities and selectivities for acetaldehyde. There is also no teaching nor appreciation of the importance of using a particular class of solvents, those containing oxygen, to direct the reaction to acetaldehyde. There is also no reference to the corrosion problem nor to the effect of the process conditions on the acetaldehyde selectivity and activity for phosphorus-containing catalysts. There is also no mention of the corrosion problem nor its solution.
In British Pat. No. 1,546,428 to Slaugh, published on May 23, 1979 are disclosed catalyst systems similar to those disclosed in the above referenced European Patent Application No. 10,373. Disclosed is a process for the preparation of ethanol by reacting hydrogen and carbon monoxide in the presence of a cobalt catalyst, a hydrocarbon solvent, a halogen ion promoter, and tertiary phosphine. The predominant product is ethanol, generally with significant amounts of other by-products such as acetic acid, methyl acetate and methane. There is no teaching showing the use of oxygen-containing solvents or diluents to obtain high activities and selectivities for acetaldehyde nor is there even disclosed the use of oxygen-containing solvents for any purpose. There is also no recognition of the corrosion problem nor is there any teaching of its solution.
In U.S. Pat. No. 4,225,517, issued Sept. 30, 1980 to Gane is disclosed a process for making acetaldehyde and ethanol. A process for making ethanol is disclosed which uses a catalyst comprising an inert liquid, cobalt, iodide or bromide and a compound containing nitrogen, phosphorus, arsenic, or antimony. In this process, ethanol is the major realizable product. Also disclosed is a process for making acetaldehyde using a system containing cobalt, an iodide or bromide, a compound containing arsenic, antimony or bismuth and various other additives. When triphenylphosphine is used in place of the arsenic, antimony or bismuth compound, ethanol is the major product. There is no disclosure of a phosphorus-containing catalyst that is highly selective to acetaldehyde, nor is there a disclosure that would lead one to such a catalyst. There is also no mention of the corrosion problem nor its solution.
None of the above references suggest or disclose the importance of maintaining particular components of a catalyst system; a source of cobalt, a halide, a phosphorus compound, and an oxygen-containing diluent or solvent; at controlled concentrations and ratios so as to enhance activity, stability and selectivity toward acetaldehyde while simultaneously minimizing equipment corrosion, as is described in the description of our invention below.